Apparatus utilizing activated carbon to adsorb solvent vapors from a flowing process air stream (from a degreaser or other plant exhaust air stream) is known. In one type of known apparatus, two tanks are provided, each tank containing a bed of activated carbon supported on a grate within the tank bottom. Solvent laden process air, ducted from the degreaser equipment through an inlet duct, is directed into one of the tanks through an inlet opening formed in a top wall thereof. Each inlet opening is selectively opened and closed to alternately connect the tanks to the inlet duct through pneumatically actuated inlet valves.
In the adsorption mode, the solvent laden air stream enters one of the adsorbing tanks through the inlet opening where the stream is forced to flow downwardly through the carbon bed which is effective to remove, by adsorption, more than 97% of the solvent vapor entering the adsorbing tank. The treated air stream then flows downwardly through the grate into the tank bottom where it exits the tank through an outlet. The outlet is connected through a pneumatically actuated valve to an outlet duct which then directs the treated air stream out of the apparatus. A main blower within the outlet duct downstream from the tank outlet induces the air flow which pulls the solvent laden air stream through the carbon bed.
In the adsorption mode of one of the tanks, the associated solvent laden air inlet and outlet valves are open while the corresponding valves of the other tank are closed. When the carbon in the bed becomes loaded to a predetermined level in the adsorbing tank, as may be detected with a hydrocarbon analyzer (e.g., a Flame Ionization Detector Monitor), the inlet and outlet valves of the adsorbing tank are closed and the corresponding valves of the other tank are opened in the adsorbing mode to switch tanks. The tank previously in the adsorbing mode now undergoes regeneration.
In the regeneration mode, steam is supplied into the bottom of the regenerating tank through a valved steam inlet pipe. As the steam flows upwardly under pressure (e.g., 9-10 psig) through the carbon bed, solvent is desorbed from the carbon by the steam. The steam then functions as a carrier gas to transport the solvent vapor through a steam exhaust pipe into a main condenser. The steam enters an exhaust manifold through a steam outlet in the top of the tank which may be opened and closed with a steam exhaust valve.
In the condenser, the steam and entrained solvent vapor are condensed by means of cooling water circulating within the condenser in a separate water cooling jacket. The cooling water enters the jacket through a cooling water inlet pipe and leaves the jacket through a cooling water outlet pipe. The water and solvent condensates collect in the condenser bottom where they drain through a bottom outlet into a conventional water separator or decanter through piping. Optionally, a secondary condenser may be disposed within the piping to condense any solvent vapors entering the piping with the condensates. In the decanter, the water (i.e., condensed steam) and solvent condensates form separate immiscible liquid layers which may be separately drained off through a water outlet and solvent outlet in a known manner.
A second condenser outlet is connected to the water separator with other piping extending between the condenser and water separator. A vent pipe open to atmosphere extends vertically from a T connector in this other piping. The vent pipe has an upper end which terminates below an opening formed in the inlet duct in vertically spaced relationship to the opening. During the steaming cycle, any solvent vapor and steam which does not condense within the condenser enters the vent pipe through the second condenser outlet and condensate entrained through the second outlet with the vapor/air flows to the separator through the other piping. Theoretically, the solvent vapor and air flow upwardly out of the vent pipe to enter the solvent laden air inlet duct through the opening. In practice, however, since the upper end of the vent pipe is not connected to the inlet duct and has a larger diameter than the opening, solvent vapor and condensate as well as water condensate leaking into the vent pipe would often be propelled through the vent pipe in an uncontrolled manner at high velocity to strike the underside of the solvent laden air inlet duct and splash against the equipment surfaces, causing corrosion, equipment damage, and pollution of the working environment with solvent vapor. Consequently, very high room concentrations of solvent vapor have been experienced around the carbon adsorbing equipment as a result of leakage through the vent pipe.
After steaming, the steam inlet valve of the tank in the regenerating mode closes, the steam exhaust valve remains open and a compressed air valve opens to direct compressed air into the bottom of the tank beneath the carbon bed. The compressed air purges the steam and solvent vapor remaining in the tank at the end of the steaming cycle to recover solvent which would otherwise be lost to atmosphere. The compressed air enters the tank at a pressure of approximately 80 psig to drive the residual steam and solvent vapor from the tank to the condenser through the steam exhaust valve where most of the steam and solvent vapor condenses and is directed by the piping to the water separator. However, particularly under these higher air purging pressures causing splashing and turbulence within the condenser, large amounts of steam and solvent vapor as well as the purging air and condensates entrained with it would enter the vent pipe and also be propelled at a high velocity out of the pipe to strike the underside of the main inlet air duct. This condensate would then splash and run downward in a random and uncontrolled manner over the carbon adsorber equipment and onto the plant floor causing corrosion and equipment damage and very high room air concentrations of solvent vapor around the adsorber equipment as aforesaid.